It is generally accepted that hyaluronan (HA), an extracellular matrix (ECM) glycosaminoglycan, is a major participant in inflammation, angiogenesis, and wound repair. Notably, HA - a simple polymer of the disaccharide D-glucuronic acid/D-N-acetylglucosamine - has differential effects on angiogenesis that are related to its chain length. Specifically, native HA, often of high molecular weight (HMW-HA) (e.g., over 1 x 103 kDa) is inhibitory to angiogenesis, whereas HA of low molecular weight (LMW-HA) (e.g., less than 3 kDa/less than 12 oligomers) stimulates angiogenesis. However, little is known about how aging affects HA and whether such effects might contribute to deficiencies in healing that are associated with aging. A better understanding of this area may lead to the development of improved therapies for wound repair in the aged. In the context of this clinical potential, we have recently found that ECM extracts from connective tissue (tendons) of aged mice contain significantly greater amounts of HA than that obtained from young mice. Moreover, we noted that dermal excisional wounds of aged mice (which heal much more slowly than wounds of young mice) and fibroblasts cultured from aged human donors produce significantly more HA than their young counterparts. These findings underscore the need for further studies that have the following objectives: (1) quantitate the influence of aging on HA concentration and molecular weight in wound tissue, (2) identify cell-mediated processes (e.g., HA synthesis/degradation) responsible for any observed changes in HA concentration and molecular weight, and (3) determine whether and how changes in HA concentration and/or molecular weight influence angiogenesis, a process critical to wound repair that is known to be deficient in aged hosts. This proposal will pursue the following 2 hypotheses: 1) age-associated increases in HA in ECM are accompanied by changes in HA molecular weight profiles that are detrimental to angiogenesis, but when stimulated, 2) endothelial cells from older donors are able to respond to pro-angiogenic forms of HA. The following 2 Specific Aims will address these 2 hypotheses: (Aim 1) determine HA concentration and molecular weight profiles in dermal excisional wound tissue and cultured wound fibroblasts isolated from young, middle aged, and aged mice and (Aim 2) determine the influence of HA molecular weight classes (high, medium, and low) on angiogenesis in vitro. For the in vitro studies, we will utilize complementary models of angiogenesis in 3D collagen: sprouting of murine microvessel explants and tubulogenesis of human microvascular endothelial cells (hmECs) isolated from donors of a range of ages. Both are previously unexamined models of HA and endothelial cell function in aging. These objectives and the associated specific aims will contribute to our long-term goal, which is to better understand age-related changes in HA in the ECM in order to examine the effect of utilizing endogenous and exogenous HA to modulate angiogenesis during tissue repair in vivo. PUBLIC HEALTH RELEVANCE: We propose that hyaluronan (HA)- a simple polymer of the disaccharide D-glucuronic acid/D-N- acetylglucosamine - is an important component of the extracellular matrix that regulates angiogenesis during tissue repair in aging. In this proposal we will use 2 related, but independent, specific aims that employ both animal and human models of aging to test the hypotheses that: 1) age-associated increases in HA in ECM are accompanied by changes in HA molecular weight profiles that are detrimental to angiogenesis, but when stimulated, 2) endothelial cells from older donors are able to respond to pro-angiogenic forms of HA. A better understanding of aged-related changes in HA in the extracellular matrix will allow for studies that exam the effect of utilizing endogenous and exogenous HA to modulate angiogenesis during tissue repair in vivo.